The present invention relates generally to color television signal generating apparatuses and more particularly to a color television signal generating apparatus comprising a camera tube, a color-resolving striped filter provided on the camera tube, and a circuit for processing a signal obtained from the camera tube.
Among the simple types of known color television cameras, there is a so-called single-tube type in which a single pickup or camera tube, having a color-resolving striped filter in its optical system, is used to generate luminance signals and color signals. Also, a color television camera has two tubes in one pickup or camera tube. One tube is used for generating luminance signals, and the other tube has a color-resolving striped filter within its optical system to generate color signals.
In either of the above mentioned color television camera types, the color-resolving striped filters are of the phase-separation or the frequency-separation system.
In a color-resolving striped filter of the phase-separation type, however, there has been the disadvantageous requirement that the color-resolving striped filter have a complicated organization, including index stripes. Another disadvantageous requirement is that a complicated has been required for generating sampling pulses on the basis of information obtained from these index stripes. A further problem is that noise results in the conversion of color information signals by a "sampling hold" of a dot-sequential system. In this system, a signal is obtained by sampling and inadvertently introducing noise of high frequency into simultaneous color information signals included in the dot-sequential. The color information signals become stretched along the time axis and are converted into noise of conspicuously low frequency, whereby the signal-to-noise ratio becomes low.
A color-resolving striped filter of the frequency-separation system does not encounter the above described difficulties accompanying a known color-resolving striped filter of the phase-separation system. However, there are interference fringes (moire), due to various causes, since two sheets of striped filters of different space frequency values are fabricated in combination. In addition, the frequency fluctuation of a carrier wave generated in the output signal, as a result of non-linearity of the deflection system of the camera tube, is a large problem. Often, there are further difficulties, such as shading due to a difference in degrees of modulation, at the peripheral region and the central region in the target surface of the camera tube.
The present applicant has previously proposed a novel "Color television signal generating apparatus" which overcomes the above described disadvantages by U.S. Pat. No. 4,041,528. This previously proposed color television signal generating apparatus comprises a color-resolving striped filter, in a camera tube, for separating the output signal of the camera tube into required signals. Detecting means detects the envelopes of specific positive wave and negative wave signals thus separated. The output of the camera tube is a superimposed signal of a direct wave signal containing signals of three primary colors, of additional mixed colors, and a high-band component signal comprising a group of modulated color signals. This camera output signal results from the amplitude modulation of a carrier wave responsive to filter stripes in the color-resolving striped filter. The carrier wave components have a high harmonic relation relative to two primary color signals. The separating means comprises first separating means for separating the direct signal from the above mentioned superimposed signal and second separating means for separating the high-band component signal. The envelope detecting means comprises a first detector for producing a demodulated output signal in accordance with an envelope resulting from a successive connection of peak values of the positive wave of the thus separated high-band component signal. A second envelope detection means produces a demodulated output signal in accordance with an envelope resulting from a successive connection of peak values of the negative wave of the thus separated high-band component signal.
However, the transmission characteristics (spectral characteristics) of the filter stripes of the color-resolving striped filter, in general, must be such that the wavelength versus response characteristic curves thereof do not mutually intersect. For this reason, it has been very difficult to mass produce color-resolving striped filters while controlling the characteristics so that the filter stripes will strictly have the desired transmission characteristics in this manner, and this difficulty has been the reason for the impossibility of producing these filters to sell at low price.